Methods and radio network nodes for measuring interference

ABSTRACT

A first radio network node ( 110 ) and a method therein for measuring interference as well as a second radio network node ( 120 ) and a method therein for enabling the first radio network node to measure interference are disclosed. The first radio network node ( 110 ) obtains ( 201 ) configuration information for indicating a designated subframe in which a reference signal for measurement of the interference is to be transmitted by the second radio network node ( 120 ). The second radio network node ( 120 ) obtains ( 202 ) configuration information for configuring a designed subframe for transmission of a reference signal. The first radio network node ( 110 ) receives ( 205 ), in the designated subframe indicated by the configuration information, the reference signal transmitted by the second radio network node ( 120 ). The first radio network node ( 110 ) determines ( 206 ) a value of the interference based on the reference signal.

TECHNICAL FIELD

The present invention relates generally to radio communication systems,such as telecommunication systems, and particularly to a first radionetwork node and a method therein for measuring interference as well asa second radio network node, and a method therein for enabling the firstradio network node to measure interference.

BACKGROUND

Time Division Duplex (TDD) is flexible in terms of possibility to adapttime resources between uplink and downlink transmissions, i.e. betweennumber of uplink and downlink subframes. By dynamically changing a ratiobetween the number of subframes for uplink and downlink, respectively,such as to match the instantaneous traffic situation, performanceexperienced by an end-user may be improved. The ratio betweenuplink/downlink subframes is determined by an uplink/downlink (UL/DL)configuration, referred to as TDD configuration hereinafter, of a radiobase station.

Another benefit of dynamic TDD is network energy savings, i.e. animprovement of downlink resource utilization allows a radio basestation, such as an evolved Node B (eNB), to configure DL subframes moreefficiently so that energy savings may be achieved.

A heterogeneous network may typically comprise macro nodes and micronodes. The macro nodes have a higher transmit power than the micronodes. In general, it is not preferable to change the TDD configurationfor the macro nodes, at least not on a small time scale. However, forheterogeneous networks, it may be that only a few user equipments (UEs)are active simultaneously per micro node, which implies a highpossibility that many neighbouring nodes, or cells, are momentarilyempty. The traffic dynamics are expected to be large with relatively lowaverage load, but high instantaneous data rates. It this case, thetraffic asymmetry between uplink and downlink directions may become asignificant. Therefore, dynamic TDD configuration becomes attractive.

When the neighbouring nodes are configured with different TDDconfigurations, interference between UL and DL including both eNB-to-eNB(DL-to-UL) and UE-to-UE (UL-to-DL) interference needs to be considered.The cross-link interference should be either mitigated or avoided sothat the benefit of dynamic TDD could be achieved.

In scenarios of dynamic uplink and downlink (UL/DL) allocation in a TDDcellular system, different neighbouring eNBs will use different TDDconfigurations from time to time. As an example, a certain cell couldbecome an ‘aggressor cell’, which uses a configuration different from aneighbouring ‘victim cell’. For instance, in a specific subframe, thereis a DL subframe of the aggressor cell, while in the same specificsubframe, there is a UL subframe for the victim cell. Hence, in thespecific subframe, the uplink of victim cell will be interfered byeNB-to-eNB interference from the aggressor cell. A problem is, hence,how to measure and estimate the eNB-to-eNB interference.

SUMMARY

One object of the solution described herein is to measure interferencebetween radio network nodes in a radio communication system.

According to one aspect, the object is achieved by a method in a firstradio network node for measuring interference between the first radionetwork node and a second radio network node. The first radio networknode obtains configuration information for indicating a designatedsubframe in which a reference signal for measurement of the interferenceis to be transmitted by the second radio network node. The designatedsubframe is designated for enabling measurement of the interference. Thefirst radio network node receives, from the second radio network node inthe designated subframe indicated by the configuration information, thereference signal. The first radio network node determines a value of theinterference based on the reference signal.

According to another aspect, the object is achieved by a first radionetwork node configured to measure interference between the first radionetwork node and a second radio network node. The first radio networknode comprises a processing circuit configured to obtain configurationinformation for indicating a designated subframe in which a referencesignal for measurement of the interference is to be transmitted by thesecond radio network node. The designated subframe is designated forenabling measurement of the interference. Furthermore, the processingcircuit is configured to receive, from the second radio network node inthe designated subframe indicated by the configuration information, thereference signal. Moreover, the processing circuit is configured todetermine a value of the interference based on the reference signal.

According to a further aspect, the object is achieved by a method in asecond radio network node for enabling a first radio network node tomeasure interference between the first radio network node and the secondradio network node. The second radio network node obtains configurationinformation for configuring a designed subframe for transmission of areference signal, the designated subframe being designated for enablingthe first radio network node to measure the interference. The secondradio network node sends, in the designated subframe, the referencesignal to the first radio network node.

According to a still further aspect, the object is achieved by a secondradio network node configured to enable a first radio network node tomeasure interference between the first radio network node and the secondradio network node. The second radio network node comprises a processingcircuit configured to obtain configuration information for configuring adesigned subframe for transmission of a reference signal. The designatedsubframe is designated for enabling the first radio network node tomeasure the interference. Furthermore, the processing circuit isconfigured to send, in the designated subframe, the reference signal tothe first radio network node.

Since both the first and second radio network nodes obtains theconfiguration information, the first and second radio network nodes arealigned, e.g. in time and/or frequency, with regard to when interferencemeasurement by the first radio network node may be performed.

Then, the first radio network node receives, in the designated subframe,the reference signal from the second radio network node. The designatedsubframe may be a flexible uplink/downlink subframe, a special subframeor the like. The special subframe is known from 3GPP terminology.

Based on the reference signal, the first radio network node determines avalue of the interference between the first and second radio networknodes. Hence, in this example, a measurement of the interference isperformed by obtaining the configuration information, receiving thereference signal and determining the value of the interference. As aresult, the above mentioned object is achieved.

Advantageously, no or little coordination between the first and secondradio network nodes is required.

Moreover, embodiments herein beneficially provide means for measuringinterference caused by different TDD configurations.

As a further advantage, the embodiments herein may be implemented whilehaving a negligible impact on Hybrid Automatic Repeat reQuest (HARQ)timing.

Furthermore, embodiments herein enable accurate eNB-to-eNB interferencemeasurements to support any eNB-to-eNB interference management scheme,such as Inter-Cell Interference Cancellation (ICIC) or the like.

Additionally, embodiments herein may for example be implemented withincurrent and/or future 3GPP specifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the embodiments disclosed herein, includingparticular features and advantages thereof, will be readily understoodfrom the following detailed description and the accompanying drawings,in which:

FIG. 1 is a schematic block diagram illustrating embodiments in anexemplifying radio communication system,

FIG. 2 is a combined signaling scheme and flowchart illustratingembodiments of the methods,

FIG. 3 is a table illustrating an aggressor cell and a victim cell,

FIG. 4 is a table illustrating exemplifying TDD configurations,

FIG. 5 is a table illustrating exemplifying TDD configurations,

FIG. 6 is a table illustrating exemplifying TDD configurations,

FIG. 7 is a block diagram illustrating an exemplifying designatedsubframe,

FIG. 8 is a block diagram illustrating an exemplifying designatedsubframe,

FIG. 9 is a flowchart illustrating embodiments of the method in thefirst radio network node,

FIG. 10 is a block diagram illustrating embodiments of the first radionetwork node,

FIG. 11 is a flowchart illustrating embodiments of the method in thesecond radio network node, and

FIG. 12 is a block diagram illustrating embodiments of the second radionetwork node.

DETAILED DESCRIPTION

Throughout the following description similar reference numerals havebeen used to denote similar elements, network nodes, parts, items orfeatures, when applicable. In the Figures, features that appear in someembodiments are indicated by dashed lines.

FIG. 1 depicts an exemplifying radio communications system 100 in whichembodiments herein may be implemented. In this example, the radiocommunications system 100 is a Long Term Evolution (LTE) system. Inother examples, the radio communication system may be any wirelesssystem including those based on 3GPP cellular communication systems,such as a Wideband Code Division Multiple Access (WCDMA) network, aGlobal System for Mobile communication (GSM network), IEEE 802.16 familyof wireless-networks standards, Worldwide Interoperability for MicrowaveAccess (WiMAX), Wireless Local Network (WLAN) or the like.

The radio communication system 100 comprises a first radio network node110 and a second radio network node 120. As used herein, the term “radionetwork node” may refer to an evolved Node B (eNB), a control nodecontrolling one or more Remote Radio Units (RRUs), a radio base station,an access point, a relay or the like. The second radio network node 120is configured to send 130 a reference signal to the first radio networknode 110.

In this example, the first radio network node 110 is configured tooperate in time division duplex mode. In other examples, the first radionetwork node 110 may be configured to operate in frequency divisionduplex mode or in a combined time/frequency duplex mode.

In this example, the second radio network node 120 is configured tooperate in time division duplex mode. In other examples, the secondradio network node 120 may be configured to operate in frequencydivision duplex mode or in a combined time/frequency duplex mode.

The first radio network node 110 may operate a first cell, such as amacro cell, and the second radio network node 120 may operate a secondcell, such as a pico or micro cell. More generally, the first and secondcells may be comprised in the radio communication system 100. In someexamples, the first and second cells are comprised in a heterogeneousnetwork comprised in the radio communication system 100.

Furthermore, a user equipment 140 is served by the first radio networknode 110. Expressed differently, the user equipment 140 may beassociated with the first cell. The user equipment 131 may transmit 150a transmission to the first radio network node 110. As used herein, theterm “user equipment” may refer to a mobile phone, a cellular phone, aPersonal Digital Assistant (PDA) equipped with radio communicationcapabilities, a smartphone, a laptop or personal computer (PC) equippedwith an internal or external mobile broadband modem, a tablet PC withradio communication capabilities, a portable electronic radiocommunication device, a sensor device equipped with radio communicationcapabilities or the like. The sensor may be any kind of weather sensor,such as wind, temperature, air pressure, humidity etc. As furtherexamples, the sensor may be a light sensor, an electronic switch, amicrophone, a loudspeaker, a camera sensor etc.

Furthermore, the radio communication system 100 comprises a networkmanagement unit 160 for controlling for example the first and secondradio network nodes 110, 120. The network management unit 160 may beconfigured to send 161 a communication signal. In some embodiments, thenetwork management unit 160 is an entity for handling information aboutsubscription of the user of the user equipment 120, about user equipmentcontext and/or about mobility of the user equipment 120, e.g. a MobilityManagement Entity (MME). In some embodiments, the network managementunit 160 is an entity responsible for operation and maintenance (O&M)tasks, e.g. an O&M node such as an Operation Support System (OSS). Insome embodiments, the network management unit 160 is an entity forhandling user plane traffic, such as a Serving Gateway (SGW). Thus, thenetwork management unit 160 may be e.g. an O&M node/system, MME or SGW.

According to embodiments herein, methods and measurement patterns foreNB-to-eNB interference measurement are described. Based on a givenmeasurement pattern, such as a transmission and reception (Tx/Rx)configuration pattern for a subframe or parts of a subframe, radionetwork nodes may measure interference without any coordination or onlylittle coordination.

FIG. 2 illustrates an exemplifying method for measuring interferencebetween the first radio network node 110 and the second radio networknode 120 when implemented in the radio communication system 100 of FIG.1.

The interference is to be measured at a carrier frequency of the firstand second radio network nodes 110, 120. In more detail, the carrierfrequency may relate to the first and second cells.

It shall be understood that the following example is given withreference to only two radio network nodes 110, 120 for the sake ofsimplicity. The embodiments herein may be readily applied to three, fouror more radio network nodes, or cells.

The following actions may be performed in any suitable order.

Action 201

In order to align, e.g. in terms of time and/or frequency, the first andsecond radio network nodes 110, 120 such that the first and second radionetwork node 110, 120 are aware of when a measurement of theinterference may be performed, action 201 and action 202 below providesthe same, or similar, configuration information to the first radionetwork node 110 and the second radio network node 120.

Thus, the first radio network node 110 obtains configuration informationfor indicating a designated subframe in which a reference signal formeasurement of the interference is to be transmitted by the second radionetwork node 120. The designated subframe is designated for enablingmeasurement of the interference. Thanks to the configuration informationthe first radio network node 110 is knows when and/or where thereference signal is sent. The configuration information is used inaction 205.

The configuration information provided to the first radio network node110 may be similar to, or corresponding to, the configurationinformation provided to the second radio network node 120 in that whenthe first radio network node 110 is in a receiving mode, in part of orin the entire designated subframe, the second radio network node 120 maybe in a transmitting mode, in part of or in the entire designatedsubframe, for transmission of reference signals. The transmission ofreference signals is described in action 205.

In some examples, the configuration information may be predetermined. Inthese examples, the first radio network node 110 may obtain theconfiguration information by determining the configuration informationbased on an identifier for identifying the first radio network node 110.

The identifier for identifying the first radio network node 110 maycomprise one or more of: a cell identity; Internet Protocol IP address;Public Land Mobile Network identity (PLMN ID); measurement periodicity;geographical information of the first radio network node 110 and thesecond radio network node 120; downlink/uplink Time Division Duplexconfiguration (DL/UL TDD configuration) or the like.

The cell identity may be a Physical Cell Identity (PCI), which providesa unique identity each cell handled by the first radio network node 110.In other examples, the cell identity is a global cell identity which isunique within the radio communication system 100.

In some other examples, the configuration information may be determinedby a central node, such as the network management unit 160. Therefore,the first radio network node 110 may obtain the configurationinformation by receiving the configuration information from the networkmanagement unit 160.

Action 202

The second radio network node 120 obtains configuration information forconfiguring a designed subframe for transmission of a reference signal.The designated subframe is designated for enabling the first radionetwork node 110 to measure the interference.

Similarly to action 201, the configuration information may bepre-determined or received from the network management unit 150.

Hence, the second radio network node 120 may obtain the configurationinformation by determining the configuration information based on anidentifier for identifying the second radio network node 120.

The identifier for identifying the second radio network node 120 maycomprise one or more of: a cell identity; Internet Protocol IP address;Public Land Mobile Network identity (PLMN ID); measurement periodicity;geographical information of the first radio network node 110 and thesecond radio network node 120; and downlink/uplink Time Division Duplexconfiguration.

Alternatively or additionally, the second radio network node 120 mayobtain the configuration information by receiving the configurationinformation from the network management unit 160.

Action 203

According to some first embodiments, the designated subframe may be aflexible uplink and/or downlink subframe. The designated subframe isdefined by that the entire subframe, or parts thereof, e.g. symbols, mayselectively, by the first radio network node 110, be put in reception ortransmission mode. As an example, the designated subframe may be aFlexible uplink/DownLink subframe (FDL subframe). The FDL subframe maybe either an uplink subframe or a downlink subframe as selected by thefirst radio network node 110. Expressed somewhat differently, the FDLsubframe may be flexibly configured into a downlink subframe or anuplink subframe by a radio network node, such as the first radio networknode 110 or the second radio network node 120.

Therefore, the configuration information may indicate to the first radionetwork node 110 that the flexible uplink and/or downlink subframe is tobe configured as an uplink subframe when the interference is to bemeasured.

The first radio network node 110 may obtain the configurationinformation by configuring the flexible uplink and/or downlink subframeas the uplink subframe indicated by the configuration information.

According to some second embodiments, the designated subframe may be aspecial subframe known from 3GPP terminology. The special subframe maycomprise an uplink timeslot, a downlink timeslot and a guard periodbetween the uplink and downlink timeslots. The term “timeslot” maycomprise one or more symbols in the time domain. Similarly, the term“guard period” may comprise one or more symbols in the time domain. Theterm “symbol” may refer to an Orthogonal Frequency-Division Multiplexing(OFDM) symbol or the like.

The configuration information may indicate to the first radio networknode 110 that the special subframe is to be configured according to asubframe configuration.

The first radio network node 110 may obtain the configurationinformation by configuring the special subframe according to thesubframe configuration indicated by the configuration information. Afirst downlink timeslot of the first radio network node (110) may beshorter than a second downlink timeslot of the second radio network node(120).

In some examples, the subframe configuration may for example be “Mode 4”in accordance with 3GPP TS 36.211. In other examples, the subframeconfiguration is any other mode according to for example 3GPP TS 36.211or similar future 3GPP specifications. Any mode is feasible, if a socalled Downlink Pilot TimeSlot (DwPTS) of the designated subframe in thesecond radio network node 120 is longer than the DwPTS of the designatedsubframe in the first radio network node 110. For example, a measuredcell, such as the second cell of the second radio network node 120, uses“Mode 1”, as specified in 3GPP TS 36.211, and a measuring cell, such asthe first cell of the first radio network node 110, uses Mode 5, is alsofeasible. Therefore, it may be said that the subframe configurationinformation for the designated subframe of the first radio network node110 may indicate a first subframe configuration according to which thefirst downlink timeslot, such as DwPTS, has a first length, or durationin e.g. ms. In connection wherewith, the subframe configurationinformation for the designated subframe of the second radio network node120 may indicate a second subframe configuration according to which thesecond downlink timeslot, such as DwPTS, has a second length, orduration in e.g. ms. The first length may be shorter than the secondlength such as to allow measurement of the interference.

In these examples, in “Mode 1”, 9 OFDM symbols are used in the measuredcell, while 3 OFDM symbols are configured in the measuring cellaccording to the specification TS 36.211. Hence, OFDM symbols 4-9 may beused for measurement.

The configuring, according to the first embodiments and/or the secondembodiments, may be performed based on a need for measurement of theinterference. As an example, if an indication of the need is above athreshold value relating to the need, then the first radio network node110 configures the designated subframe as the uplink subframe, wherebyreception, in action 205, of the reference signal is enabled. In turn,this implies that action 206 may be performed.

The need may occur due to that the value of the interference value isold, i.e. the time past since last determination of the value, seeaction 206, is above a threshold value.

In other examples, the need may occur when a Block Error Rate (BLER) isabove a threshold value for BLER. That is to say the BLER is bad. TheBLER may be said to be good when the BLER is below the threshold valuefor BLER.

For example, if BLER is good and there is a lot of data to transmit, themeasuring node may decide to use the designated subframe in whichmeasurement is possible for downlink transmission, for example towardsthe user equipment 140, instead.

Similarly, for example, if BLER is good and there is a lot of data toreceive, the first radio network node 100 may decide to use thedesignated subframe for uplink transmission from the user equipment 140instead of transmission of reference signals from the second radionetwork node 120.

In other examples, the value of the interference is used forinterference management. During for example a low load scenario or foruser equipments in the so called cell range extension, the designatedsubframe may be configured into an uplink subframe, which may be acompletely empty subframe if desired. In contrast, CRS is alwaystransmitted in a downlink subframe. Thus, if the designated subframe isconfigured as an uplink subframe the interference may be reduced thanksto that no CRS is transmitted. With this configuration, no interferencecomes from this subframe.

Action 204

According to some first embodiments, the designated subframe maycomprise a flexible uplink and/or downlink subframe.

The configuration information may indicate to the second radio networknode 120 that the flexible uplink and/or downlink subframe is to beconfigured as a downlink subframe.

In these embodiments, the second radio network node 120 may obtain theconfiguration information by configuring the flexible uplink and/ordownlink subframe as the downlink subframe indicated by theconfiguration information.

According to some second embodiments, the designated subframe may be aspecial subframe. The special subframe may comprise an uplink timeslot,a downlink timeslot and a guard period between the uplink and downlinktimeslots.

The configuration information may indicate to the second radio networknode 120 that the special subframe is to be configured according to asubframe configuration. The first downlink timeslot of the first radionetwork node (110) may be shorter than the second downlink timeslot ofthe second radio network node (120).

In these embodiments, the second radio network node 120 may obtain theconfiguration information by configuring the special subframe accordingto the subframe configuration indicated by the configurationinformation.

It may be noted that according to preferred embodiments, the secondradio network node 120 does always transmit the reference signal. Thus,the decision on whether or not to perform a measurement is left solelyto the first radio network node 110. In contrast, the first radionetwork node 110 performs action 203 based on the need for measurementof the interference as explained above.

Action 205

In order to measure the interference, e.g. from the second radio networknode 120 towards the first radio network node 110, the second radionetwork node 120 sends, in the designated subframe, the reference signalto the first radio network node 110.

As explained above in conjunction with action 203, it is up to the firstradio network node 110 to decide whether or not to configure, at leastpartially, the designated subframe for reception of the referencesignal. Again, when the designated subframe is partially configured forreception, some symbols of the designated subframe are uplink symbols,i.e. reception is possible, and some symbols of the designated subframeare downlink symbols. Also as mentioned, the designated subframe may bean uplink subframe, in which reception is possible.

Action 206

The first radio network node 110 determines a value of the interferencebased on the reference signal. In this manner, the first radio networknode 110 completes, or finalizes, the measurement of the interference.

The value of the interference may be represented by one or more of: aChannel Quality Indicator (CQI), aSignal-to-Interference-and-Noise-Ratio (SINR), aSignal-to-Interference-Ratio (SIR), a Signal-to-Noise-Ratio (SNR), aReference Signal Received Power (RSRP), a Reference Signal ReceivedQuality (RSRQ), a Received Signal Strength Indicator (RSSI) and thelike.

The first radio network node 110 may need to obtain information abouttransmission power of the reference signals from the second radionetwork node according to known methods.

Action 207

The first radio network node 110 may adapt transmit power, Tx power, ofthe first radio network node 110 based on the value. Typically, when thevalue of interference is above a threshold for the value ofinterference, the transmit power of the first radio network node 110 isincreased. Likewise, when the value of interference is below thethreshold for the value of interference, the transmit power of the firstradio network node 110 may be decreased.

If action 207 is performed, thus adjusting Tx power of the first radionetwork node 110, it may be that it is not necessary to also adjust theTx power of the second radio network node 120 as in action 209. Hence,action 208 and 209 need not be performed after action 207 has beenperformed. Advantageously, less information is transmitted.

Action 208

The first radio network node 110 may send the value of the interferenceto the second radio network node 120. Thereby, the second radio networknode 120 may use the value in action 209.

The value of the interference may be represented by one or more of:Channel Quality Indicator, Signal-to-Interference-and-Noise-Ratio,Signal-to-Interference-Ratio, Signal-to-Noise-Ratio, Reference SignalReceived Power, Reference Signal Received Quality, and Received SignalStrength Indicator and the like.

Action 209

The second radio network node 120 may adapt transmit power of the secondradio network node 120 based on the value. Typically, when the value ofinterference is above a second threshold for the value of interference,the transmit power of the second radio network node 120 is decreased.Likewise, when the value of interference is below the second thresholdfor the value of interference, the transmit power of the second radionetwork node 120 may be increased.

Some further details with reference to action 203 and 204 will now bedescribed.

In order to measure eNB-to-eNB interference at the designated subframe,the second radio network node 120 shall be in Tx mode, i.e. at least thesymbol(s) carrying the reference signal shall be in Tx mode. The firstradio network node 110 shall be to be in Rx mode, i.e. at least thosesymbols during which the reference signal is sent by the second radionetwork node 120 shall be in Rx mode. Therefore, Tx and Rx modes insubframes of different cells are relevant each other for the measurementof the interference. The alignment of the Tx/Rx modes of the first andsecond radio network nodes 110, 120, e.g. a measured cell and ameasuring cell, is necessary.

In order to align the Tx/Rx modes without a real-time onlinecoordination during operation, it is herein described how the Tx/Rxmodes of different cells at the designated subframe, and possibly alsoat a specific radio frame number, may be pre-defined according to thecell identifier, TDD configuration and other parameters, e.g. PLMN ID,IP address or the like.

The specific radio frame number i of DL Tx for the measured cell isdefined as follows:i=ƒ ₁(id,M,DL/ULconf,Timing)where id may be a physical cell identifier (PCI), IP address, PLMN ID orany identifier which can identify the measured cell, M is themeasurement period, and DL/UL conf is the DL/UL TDD configuration andspecial subframe configuration, Timing refers to global timing, i.e,obtained from GPS, or from core network. One simple example of thefunction ƒ₁(•) is:i=(cellid+k*N)mod(1024)k=0,1, . . .N is a pre-set periodicity, and the periodicity can be from seconds tominutes, or even hours. The period can be set according to theeNB-to-eNB interference time-domain variation characteristics.

In the corresponding subframe, and optionally also radio frame number,given above, the measuring cell can be configured into Rx mode toestimate eNB-to-eNB interference.

In general, the above method may be extended to a method based ongeographical information of each eNBs instead of PCI or any otheridentification number other than PCI.

FIG. 3 shows exemplifying TTD configurations for the first cell “Cell 1”and the second cell “Cell 2”. The terms “victim cell” and “aggressorcell” are explained and illustrated. In the Figure, a radio frame 0“Radio Frame 0” comprises 10 subframes, denoted by reference numerals0-9. In a fourth subframe 4 the first cell “Cell 1” is configured withan uplink subframe U and the second cell “Cell 2” is configured with adownlink subframe D. Thereby, the first cell may receive transmissionfrom the second cell. This means that the first cell becomes a victimcell and the second cell becomes an aggressor cell. Additionally,special subframes S are shown in subframe 1 and 6.

FIG. 4 illustrates an exemplifying TDD configuration according to thefirst embodiments, in which the designated subframe may be a FDLsubframe. The same or similar reference numerals denote the same orsimilar cells, radio frames or the like as in FIG. 3.

In this example, subframe 4 is a pre-determined, or pre-set, subframefor flexible DL/UL. In order to measure eNB-to-eNB interference, inradio frame m, cell 2 operates in DL according to aforementioned TDDconfiguration, while cell 1 is configured to either DL or UL asdetermined by the first radio network node 110, e.g. depending ontraffic status, or load on the first cell. If cell 1, e.g. the firstradio network node 110, needs to estimate interference between Cell 2 toits own cell “Cell 1”, at the corresponding subframe, it is configuredinto an UL subframe for receiving the reference signal from the secondcell, e.g. the second radio network node 120.

Similarly, in another radio frame occasions, i.e., radio frame k, Cell 1is predetermined to Tx for DL and the second cell is configured to be ULif interference estimation is needed. Otherwise, the configurations canbe flexible.

FIG. 5 illustrates an exemplifying TDD configuration according to thesecond embodiments, in which the designated subframe may be a specialsubframe. The same or similar reference numerals denote the same orsimilar cells, radio frames or the like as in FIG. 3.

As an example, at a special subframe S of radio frame m in subframe 1, afirst number of DL OFDM symbols of cell 2 are configured. Furthermore, asecond number of DL OFM symbols of cell 1 are configured. Here, thefirst number of DL OFDM symbols is greater than the second number of DLOFDM symbols. In one or more of the subframes corresponding to those DLOFDM symbols which are in excess compared to the second number of DLOFDM symbols, the first cell may measure eNB-to-eNB interferencemeasurement. In another radio frame, i.e., radio frame k, more DL OFDMsymbols are configured in the special subframe of cell 1, and thus thesecond cell may conduct eNB-to-eNB interference measurement when needed.

FIG. 6 illustrates an exemplifying TDD configuration according to thefirst embodiments, in which the designated subframe may be a FDLsubframe. The same or similar reference numerals denote the same orsimilar cells, radio frames or the like as in FIG. 3.

As shown in FIG. 6, the first radio network node 110, “Measuring node”,may wish to measure the eNB-to-eNB interference from the second radionetwork node 120 “Measured node”. Assume subframe 4 is the FDL subframe,the following configuration and procedure may be used for eNB-to-eNBinterference measurement.

A Tx/Rx configuration pattern relates to a pattern according to whichthe designated subframe is configured as a DL subframe, wherebymeasurement by the first radio network node 110 is possible. In thisexample, the Tx/Rx configuration pattern is applied, by the second radionetwork node 120, to the FDL subframe.

The Tx/Rx configuration pattern for the FDL subframe may bepredetermined by utilizing the identifier based alignment as describedin action 201 and 202 in FIG. 2. Hence, no further coordination betweenthe first and second radio network nodes is required.

Alternatively or additionally, the Tx/Rx configuration pattern for theFDL subframe may be determined by coordination/mutual negotiationsbetween the first and second radio network nodes 110, 120.

According to the Tx/Rx configuration pattern determined, the secondradio network node 120 has configured the FDL subframe as a DL subframe.See subframe 4 of cell 2. In this DL subframe, the reference signal,such as a Cell-specific Reference Signal (CRS), a Channel StateInformation Reference Signal (CSI-RS) or the like, is transmitted.

For the first radio network node 110, the FDL subframe is configuredinto UL subframe for reception of the reference signal when needed. Inthis UL subframe, the first radio network node 110 is in Rx mode. Thefirst radio network node 110 estimates the eNB-to-eNB interference fromthe reference signal (RS) transmitted by the second radio network node.

FIGS. 7 and 8 show exemplifying designated subframes according to thesecond embodiment.

In FIG. 7, an example of the special subframe is shown. The first radionetwork node 110 “Measuring node” may wish to measure the eNB-to-eNBinterference from the second radio network node 120 “Measured node”.Then, the following configuration and procedure may be used foreNB-to-eNB interference measurement.

The Tx/Rx configuration pattern for the special subframe may bepredetermined by utilizing the identifier based alignment as describedin action 201 and 202 in FIG. 2. Hence, no further coordination betweenthe first and second radio network nodes is required.

Alternatively or additionally, the Tx/Rx configuration pattern for thespecial subframe may be determined by coordination/mutual negotiationsbetween the first and second radio network nodes 110, 120.

According to the Tx/Rx configuration pattern determined, the secondradio network node 120 transmits the reference signal in a certainspecial subframe, for example in a DwPTS time slot at a TD-LTE frame.This special subframe configuration is set as mode 4 and is standardizedin LTE specification TS36.211.

Other special sub-frame configurations, according to for exampleTS36.211, can also be used if there are enough available referencesignals in the corresponding configuration. The structure of the specialsub-frame is illustrated in FIG. 7 with a normal cyclic prefix.

Now referring to FIG. 8, for the first radio network node 110, OFDMsymbol 0 to 2 are the so called Downlink Pilot TimeSlot (DwPTS) in thespecial subframe. This means that OFDM symbol 0 to 2 are DL symbols. Incontrast, OFDM symbol 13^(th) is an UL symbol, and OFDM symbol 12^(th)GP is a guard period, i.e. here just one symbol, for switching fromdownlink to uplink. The GP duration is much longer than that of thesecond radio network node 120, during most of which the second radionetwork node 120 conducts a DL Tx.

Thus, the first radio network node 110 may receive the OFDM symbol 3 to11 sent from the second radio network node 120, where OFDM symbol 4, 7and 11 have the DL cell specific reference signal (CRS) or otherreference signals. Then first radio network node 110 can estimate signalstrength of second radio network node 120 by processing received signalsat OFDM symbol 4, 7 and 11. The configuration in FIG. 8 is just oneexample. The guard period (GP) can be reduced according to the network.If the guard period is reduced, less OFDM symbols may be used forinterference measurement, or interference estimation.

After the eNB-to-eNB interference is estimated according any one of theexamples described herein, e.g. with reference to FIG. 6 or FIGS. 7 and8, the first radio network node 110 may signal, or send, the measurementresults, i.e. the value of the interference, to the second radio networknode 120 e.g. via a backhaul connection such as X2 link. See action 208.The second radio network node 120 takes action to handle transmit powercontrol based on the feedback in terms of the value of the interference.See action 209.

By exploiting channel reciprocity, the first radio network node 110 mayalso adapt its own power control strategy based on the value of theinterference. In this manner, the first radio network node 110 controlsits own Tx power to reduce the interference towards the second radionetwork node 120 based on e.g. a pre-defined rule. See action 207. Inprinciple, any pair of radio network nodes only need only onemeasurement if the radio communication system 100 is homogeneous,whereby channel reciprocity is maintained and reliable.

With reference to FIG. 9, embodiments of the method in the first radionetwork node 110 for measuring interference between the first radionetwork node 110 and the second radio network node 120 are described.

The following actions may be performed in any suitable order.

Action 901

The first radio network node 110 obtains configuration information forindicating a designated subframe in which a reference signal formeasurement of the interference is to be transmitted by the second radionetwork node 120. The designated subframe is designated for enablingmeasurement of the interference. This action is similar to action 201.

The first radio network node 110 may obtain the configurationinformation by determining the configuration information based on anidentifier for identifying the first radio network node 110.

The identifier for identifying the first radio network node 110 maycomprise one or more of: a cell identity; Internet Protocol IP address;Public Land Mobile Network identity; measurement periodicity;geographical information of the first radio network node 110 and thesecond radio network node 120; and downlink/uplink Time Division Duplexconfiguration.

The first radio network node 110 may obtain the configurationinformation by receiving the configuration information from the networkmanagement unit 160.

Action 902

According to the first embodiments, the designated subframe may be aflexible uplink and/or downlink subframe.

The configuration information may indicate to the first radio networknode 110 that the flexible uplink and/or downlink subframe is to beconfigured as an uplink subframe when the interference is to bemeasured.

The first radio network node 110 may obtain the configurationinformation by configuring the flexible uplink and/or downlink subframeas the uplink subframe indicated by the configuration information.

The configuring may be performed based on a need for measurement of theinterference.

According to the second embodiments, the designated subframe may be aspecial subframe. The special subframe may comprise an uplink timeslot,a downlink timeslot and a guard period between the uplink and downlinktimeslots.

The configuration information may indicate to the first radio networknode 110 that the special subframe is to be configured according to asubframe configuration.

The first radio network node 110 may obtain the configurationinformation by configuring the special subframe according to thesubframe configuration indicated by the configuration information. Afirst downlink timeslot of the first radio network node (110) may beshorter than a second downlink timeslot of the second radio network node(120).

The configuring may be performed based on a need for measurement of theinterference.

This action is similar to action 203.

Action 903

The first radio network node 110 receives, from the second radio networknode 120 in the designated subframe indicated by the configurationinformation, the reference signal. This action is similar to action 205.

Action 904

The first radio network node 110 determines a value of the interferencebased on the reference signal. This action is similar to action 206.

The value of the interference may be represented by one or more of:Channel Quality Indicator, Signal-to-Interference-and-Noise-Ratio,Signal-to-Interference-Ratio, Signal-to-Noise-Ratio, Reference SignalReceived Power, Reference Signal Received Quality, and Received SignalStrength Indicator and the like.

Action 905

The first radio network node 110 may adapt transmit power, Tx power, ofthe first radio network node 110 based on the value. This action issimilar to action 207.

Action 906

The first radio network node 110 may send the value of the interferenceto the second radio network node 120. This action is similar to action208.

With reference to FIG. 10, embodiments of the first radio network node110 when configured to perform the embodiments described herein. Thus,the network node 110, 111, 112 is configured to measure interferencebetween the first radio network node 110 and the second radio networknode 120.

The first radio network node 110 comprises a processing circuit 1010configured to obtain configuration information for indicating adesignated subframe in which a reference signal for measurement of theinterference is to be transmitted by the second radio network node 120.The designated subframe is designated for enabling measurement of theinterference.

Furthermore, the processing circuit 1010 is configured to receive, fromthe second radio network node 120 in the designated subframe indicatedby the configuration information, the reference signal. Moreover, theprocessing circuit 1010 is configured to determine a value of theinterference based on the reference signal.

The processing circuit 1010 may further be configured to determine theconfiguration information based on an identifier for identifying thefirst radio network node 110.

The processing circuit 1010 may further be configured to receive theconfiguration information from a network management unit 160.

The processing circuit 1010 may further be configured to send the valueof the interference to the second radio network node 120.

The processing circuit 1010 may be a processing unit, a processor, anapplication specific integrated circuit (ASIC), a field-programmablegate array (FPGA) or the like. As an example, a processor, an ASIC, anFPGA or the like may comprise one or more processor kernels.

The identifier for identifying the first radio network node 110 maycomprise one or more of: a cell identity; Internet Protocol IP address;Public Land Mobile Network identity; measurement periodicity;geographical information of the first radio network node 110 and thesecond radio network node 120; and downlink/uplink Time Division Duplexconfiguration.

The value of the interference may be represented by one or more of: aChannel Quality Indicator, a Signal-to-Interference-and-Noise-Ratio, aSignal-to-Interference-Ratio, a Signal-to-Noise-Ratio, a ReferenceSignal Received Power, a Reference Signal Received Quality, and aReceived Signal Strength Indicator and the like.

The designated subframe may be a flexible uplink and/or downlinksubframe.

The configuration information may indicate to the first radio networknode 110 that the flexible uplink and/or downlink subframe is to beconfigured as an uplink subframe when the interference is to bemeasured.

The processing circuit 1010 may further be configured to configure theflexible uplink and/or downlink subframe as the uplink subframeindicated by the configuration information.

The processing circuit 1010 may further be configured to configure theflexible uplink and/or downlink subframe as the uplink subframeindicated by the configuration information based on a need formeasurement of the interference.

The designated subframe may be a special subframe. The special subframemay comprise an uplink timeslot, a downlink timeslot and a guard periodbetween the uplink and downlink timeslots.

The configuration information may indicate to the first radio networknode 110 that the special subframe is to be configured according to asubframe configuration,

The processing circuit 1010 may further be configured to configure thespecial subframe according to the subframe configuration indicated bythe configuration information. A first downlink timeslot of the firstradio network node (110) may be shorter than a second downlink timeslotof the second radio network node (120).

The first radio network node 110 according to claim 33, wherein theprocessing circuit 1010 further is configured to configure the specialsubframe according to the subframe configuration indicated by theconfiguration information based on a need for measurement of theinterference.

The processing circuit 1010 may further be configured to adapt transmitpower of the first radio network node 110 based on the value.

The first radio network node 110 further comprises a transmitter 1020,which may be configured to send one or more of the value of interferenceand other numbers, values or parameters described herein.

The first radio network node 110 further comprises a receiver 1030,which may be configured to receive one or more of the reference signaland other numbers, values or parameters described herein.

The first radio network node 110 further comprises a memory 1040 forstoring software to be executed by, for example, the processing circuit.The software may comprise instructions to enable the processing circuitto perform the method in the first radio network node 110 as describedabove in conjunction with FIGS. 2 and/or 9. The memory may be a harddisk, a magnetic storage medium, a portable computer diskette or disc,flash memory, random access memory (RAM) or the like. Furthermore, thememory may be an internal register memory of a processor.

FIG. 11 illustrates embodiments of the method in the second radionetwork node 120 for enabling a first radio network node 110 to measureinterference between the first radio network node 110 and the secondradio network node 120.

The following actions may be performed in any suitable order.

Action 1101

The second radio network node 120 obtains configuration information forconfiguring a designed subframe for transmission of a reference signal,the designated subframe being designated for enabling the first radionetwork node 110 to measure the interference. This action is similar toaction 202.

The second radio network node 120 may obtain the configurationinformation by determining the configuration information based on anidentifier for identifying the second radio network node 120.

The identifier for identifying the first radio network node 110 maycomprise one or more of: a cell identity; Internet Protocol IP address;Public Land Mobile Network identity, “PLMN ID”; measurement periodicity;geographical information of the first radio network node 110 and thesecond radio network node 120; and downlink/uplink Time Division Duplexconfiguration, “DL/UL TDD configuration” and the like.

The second radio network node 120 may obtain the configurationinformation by receiving the configuration information from a networkmanagement unit 160.

Action 1102

According to some first embodiments, the designated subframe maycomprise a flexible uplink and/or downlink subframe.

The configuration information may indicate to the second radio networknode 120 that the flexible uplink and/or downlink subframe is to beconfigured as a downlink subframe.

In these embodiments, the second radio network node 120 may obtain theconfiguration information by configuring the flexible uplink and/ordownlink subframe as the downlink subframe indicated by theconfiguration information.

According to some second embodiments, the designated subframe may be aspecial subframe. The special subframe may comprise an uplink timeslot,a downlink timeslot and a guard period between the uplink and downlinktimeslots.

The configuration information may indicate to the second radio networknode 120 that the special subframe is to be configured according to asubframe configuration. A first downlink timeslot of the first radionetwork node (110) may be shorter than a second downlink timeslot of thesecond radio network node (120).

In these embodiments, the second radio network node 120 may obtain theconfiguration information by configuring the special subframe accordingto the subframe configuration indicated by the configurationinformation.

This action is similar to action 204.

Action 1103

The second radio network node 120 sends, in the designated subframe, thereference signal to the first radio network node 110. This action issimilar to action 205.

Action 1104

The second radio network node 120 may receive a value of theinterference. This action is similar to action 208.

The value of the interference may be represented by one or more of:Channel Quality Indicator, Signal-to-Interference-and-Noise-Ratio,Signal-to-Interference-Ratio, Signal-to-Noise-Ratio, Reference SignalReceived Power, Reference Signal Received Quality, Received SignalStrength Indicator and the like.

Action 1105

The second radio network node 120 may adapt transmit power of the secondradio network node 120 based on the value. This action is similar toaction 209.

FIG. 12 illustrates embodiments of the second radio network node 120when configured to perform the embodiments described herein. Thus, thesecond radio network node 120 is configured to enable a first radionetwork node 110 to measure interference between the first radio networknode 110 and the second radio network node 120.

The second radio network node 120 comprises a processing circuit 1210configured to obtain configuration information for configuring adesigned subframe for transmission of a reference signal. The designatedsubframe is designated for enabling the first radio network node 110 tomeasure the interference. Furthermore, the processing circuit 1210 isconfigured to send, in the designated subframe, the reference signal tothe first radio network node 110.

The processing circuit 1210 may further be configured to determine theconfiguration information based on an identifier for identifying thesecond radio network node 120.

The processing circuit 1210 may further be configured to receive theconfiguration information from a network management unit 160.

The processing circuit 1210 may further be configured to receive a valueof the interference; and adapt transmit power of the second radionetwork node 120 based on the value.

The processing circuit 1210 may be a processing unit, a processor, anapplication specific integrated circuit (ASIC), a field-programmablegate array (FPGA) or the like. As an example, a processor, an ASIC, anFPGA or the like may comprise one or more processor kernels.

The identifier for identifying the first radio network node 110 maycomprise one or more of: a cell identity; Internet Protocol IP address;Public Land Mobile Network identity; measurement periodicity;geographical information of the first radio network node 110 and thesecond radio network node 120; and downlink/uplink Time Division Duplexconfiguration.

The value of the interference may be represented by one or more of: aChannel Quality Indicator, a Signal-to-Interference-and-Noise-Ratio, aSignal-to-Interference-Ratio, a Signal-to-Noise-Ratio, a ReferenceSignal Received Power, a Reference Signal Received Quality, and aReceived Signal Strength Indicator and the like.

In some embodiments, the designated subframe may be a flexible uplinkand/or downlink subframe.

The configuration information may indicate to the second radio networknode 120 that the flexible uplink and/or downlink subframe is to beconfigured as a downlink subframe

In these embodiments, the processing circuit 1210 may further beconfigured to configure the flexible uplink and/or downlink subframe asthe downlink subframe indicated by the configuration information.

In some embodiments, the designated subframe may be a special subframe.The special subframe may comprise an uplink timeslot, a downlinktimeslot and a guard period between the uplink and downlink timeslots.

The configuration information may indicate to the second radio networknode 120 that the special subframe is to be configured according to asubframe configuration.

In these embodiments, the processing circuit 1210 may further beconfigured to configure the special subframe according to the subframeconfiguration indicated by the configuration information. A firstdownlink timeslot of the first radio network node (110) may be shorterthan a second downlink timeslot of the second radio network node (120).

The second radio network node 120 further comprises a transmitter 1220,which may be configured to send one or more of the reference signal andother numbers, values or parameters described herein.

The second radio network node 120 further comprises a receiver 1230,which may be configured to receive one or more of the value ofinterference and other numbers, values or parameters described herein.

The second radio network node 120 further comprises a memory 1240 forstoring software to be executed by, for example, the processing circuit.The software may comprise instructions to enable the processing circuitto perform the method in the second radio network node 120 as describedabove in conjunction with FIGS. 2 and/or 11. The memory may be a harddisk, a magnetic storage medium, a portable computer diskette or disc,flash memory, random access memory (RAM) or the like. Furthermore, thememory may be an internal register memory of a processor.

As used herein, the terms “number”, “value” may be any kind of digit,such as binary, real, imaginary or rational number or the like.Moreover, “number”, “value” may be one or more characters, such as aletter or a string of letters. “number”, “value” may also be representedby a bit string.

Even though embodiments of the various aspects have been described, manydifferent alterations, modifications and the like thereof will becomeapparent for those skilled in the art. The described embodiments aretherefore not intended to limit the scope of the present disclosure.

The invention claimed is:
 1. A method in a first radio network node formeasuring interference between the first radio network node and a secondradio network node, the method comprising: obtaining configurationinformation that indicates which subframe is a designated subframe inwhich a reference signal for measurement of the interference is to betransmitted by the second radio network node, the designated subframebeing designated for enabling measurement of the interference, whereinthe designated subframe is a flexible uplink and/or downlink subframe;dynamically configuring the designated subframe in the first radionetwork node as an uplink subframe according to the obtainedconfiguration information when the interference is to be measured,wherein the designated subframe is configured in the entirety or partsthereof; receiving, from the second radio network node in the designatedsubframe indicated by the configuration information, the referencesignal; and determining a value of the interference based on thereference signal.
 2. The method according to claim 1, wherein theobtaining of the configuration information comprises determining theconfiguration information based on an identifier for identifying thefirst radio network node, wherein the identifier for identifying thefirst radio network node comprises one or more of: a cell identity;Internet Protocol address; Public Land Mobile Network identity;measurement periodicity; geographical information of the first radionetwork node and the second radio network node; and downlink/uplink TimeDivision Duplex configuration.
 3. The method according to claim 1,wherein the obtaining of configuration information comprises receivingthe configuration information from a network management unit.
 4. Themethod according to claim 1, wherein the value of the interference isrepresented by one or more of: Channel Quality Indicator,Signal-to-Interference-and-Noise-Ratio, Signal-to-Interference-Ratio,Signal-to-Noise-Ratio, Reference Signal Received Power, Reference SignalReceived Quality, and Received Signal Strength Indicator.
 5. The methodaccording to claim 1, said flexible uplink and/or downlink subframebeing adaptively configured as one of an uplink subframe and a downlinksubframe as selected by the first or the second radio network node. 6.The method according to claim 5, wherein the configuring is performedbased on a need for measurement of the interference.
 7. The methodaccording to claim 1, further comprising: adapting a transmit power ofthe first radio network node based on the value.
 8. The method accordingto claim 1, further comprising: sending the value of the interference tothe second radio network node.
 9. A method in a second radio networknode for enabling a first radio network node to measure interferencebetween the first radio network node and the second radio network node,the method comprising: obtaining configuration information forconfiguring a designated subframe for transmission of a referencesignal, the designated subframe being designated for enabling the firstradio network node to measure the interference, wherein the designatedsubframe is a flexible uplink and/or downlink subframe, and wherein theconfiguration information indicates to the second radio network nodethat the designated subframe is to be configured as a downlink subframe;configuring the designated subframe as the downlink subframe indicatedby the configuration information; and sending, in the designatedsubframe, the reference signal to the first radio network node.
 10. Themethod according to claim 9, wherein the identifier for identifying thefirst radio network node comprises one or more of: a cell identity;Internet Protocol address; Public Land Mobile Network identity;measurement periodicity; geographical information of the first radionetwork node and the second radio network node; and downlink/uplink TimeDivision Duplex configuration.
 11. The method according to claim 9,wherein the obtaining of configuration information comprises receivingthe configuration information from a network management unit.
 12. Themethod according to claim 9, said flexible uplink and/or downlinksubframe being adaptively configured as one of an uplink subframe and adownlink subframe as selected by the first or the second radio networknode.
 13. The method according to claim 9, further comprising: receivinga value of the interference; and adapting transmit power of the secondradio network node based on the value.
 14. The method according to claim13, wherein the value of the interference is represented by one or moreof: a Channel Quality Indicator, aSignal-to-Interference-and-Noise-Ratio, a Signal-to-Interference-Ratio,a Signal-to-Noise-Ratio, a Reference Signal Received Power, a ReferenceSignal Received Quality, and a Received Signal Strength Indicator.
 15. Afirst radio network node configured to measure interference between thefirst radio network node and a second radio network node, wherein thefirst radio network node comprises a processing circuit configured to:obtain configuration information that indicates which subframe is adesignated subframe in which a reference signal for measurement of theinterference is to be transmitted by the second radio network node, thedesignated subframe being designated for enabling measurement of theinterference, wherein the designated subframe is a flexible uplinkand/or downlink subframe; dynamically configure the designated subframein the first radio network node as an uplink subframe according to theobtained configuration information when the interference is to bemeasured, wherein the designated subframe is configured in the entiretyor parts thereof; receive, from the second radio network node in thedesignated subframe indicated by the configuration information, thereference signal; and determine a value of the interference based on thereference signal.
 16. The first radio network node according to claim15, wherein the identifier for identifying the first radio network nodecomprises one or more of: a cell identity; Internet Protocol address;Public Land Mobile Network identity; measurement periodicity;geographical information of the first radio network node and the secondradio network node; and downlink/uplink Time Division Duplexconfiguration.
 17. The first radio network node according to claim 15,wherein the processing circuit is further configured to receive theconfiguration information from a network management unit.
 18. The firstradio network node according to claim 15, wherein the value of theinterference is represented by one or more of: a Channel QualityIndicator, a Signal-to-Interference-and-Noise-Ratio, aSignal-to-Interference-Ratio, a Signal-to-Noise-Ratio, a ReferenceSignal Received Power, a Reference Signal Received Quality, and aReceived Signal Strength Indicator.
 19. The first radio network nodeaccording to claim 15, wherein said flexible uplink and/or downlinksubframe being adaptively configured as one of an uplink subframe and adownlink subframe as selected by the first or the second radio networknode.
 20. The first radio network node according to claim 19, whereinthe processing circuit is further configured to configure the flexibleuplink and/or downlink subframe as the uplink subframe indicated by theconfiguration information based on a need for measurement of theinterference.
 21. The first radio network node according to claim 15,wherein the processing circuit is further configured to adapt transmitpower of the first radio network node based on the value.
 22. The firstradio network node according to claim 15, wherein the processing circuitis further configured to send the value of the interference to thesecond radio network node.
 23. A second radio network node configured toenable a first radio network node to measure interference between thefirst radio network node and the second radio network node, the secondradio network node comprising a processing circuit configured to: obtainconfiguration information for configuring a designated subframe fortransmission of a reference signal, the designated subframe beingdesignated for enabling the first radio network node to measure theinterference, wherein the designated subframe is a flexible uplinkand/or downlink subframe, and wherein the configuration informationindicates to the second radio network node that the designated subframeis to be configured as a downlink subframe; configure the flexibleuplink and/or downlink subframe as the downlink subframe indicated bythe configuration information; and send, in the designated subframe, thereference signal to the first radio network node.
 24. The second radionetwork node according to claim 23, wherein the identifier foridentifying the first radio network node comprises one or more of: acell identity; Internet Protocol address; Public Land Mobile Networkidentity; measurement periodicity; geographical information of the firstradio network node and the second radio network node; anddownlink/uplink Time Division Duplex configuration.
 25. The second radionetwork node according to claim 23, wherein the processing circuit isfurther configured to receive the configuration information from anetwork management unit.
 26. The second radio network node according toclaim 23, said flexible uplink and/or downlink subframe being adaptivelyconfigured as one of an uplink subframe and a downlink subframe asselected by the first or the second radio network node.
 27. The secondradio network node according to claim 23, wherein the processing circuitis further configured to receive a value of the interference; and adapttransmit power of the second radio network node based on the value. 28.The second radio network node according to claim 27, wherein the valueof the interference is represented by one or more of: a Channel QualityIndicator, a Signal-to-Interference-and-Noise-Ratio, aSignal-to-Interference-Ratio, a Signal-to-Noise-Ratio, a ReferenceSignal Received Power, a Reference Signal Received Quality, and aReceived Signal Strength Indicator.
 29. The method of claim 1, whereinsaid obtaining comprises obtaining the configuration information withoutreal-time, online coordination between the first and second radionetwork nodes.
 30. The method of claim 1, wherein the designatedsubframe is predetermined according to the identifier and a timedivision duplex (TDD) configuration of the first radio network node. 31.The method of claim 1, wherein said dynamically configuring comprisesdetermining whether the designated subframe in the first radio networknode is to be configured as an uplink subframe or a downlink subframe,depending on whether interference is to be measured in the designatedsubframe.
 32. The first radio network node of claim 15, wherein theprocessing circuit is configured to obtain the configuration informationwithout real-time, online coordination between the first and secondradio network nodes.
 33. The first radio network node of claim 15,wherein the designated subframe is predetermined according to theidentifier and a time division duplex (TDD) configuration of the firstradio network node.
 34. The first radio network node of claim 15,wherein the processing circuit is configured to dynamically configurethe designated subframe as an uplink subframe by determining whether thedesignated subframe in the first radio network node is to be configuredas an uplink subframe or a downlink subframe, depending on whetherinterference is to be measured in the designated subframe.